def test_graph_conversions():
igraph = ig.Graph.Star(6)
g = Graph.from_igraph(igraph)
assert g.n_nodes == igraph.vcount()
assert g.edges() == igraph.get_edgelist()
assert all(c == 0 for c in g._edge_colors)
nxg = nx.star_graph(5)
g = Graph.from_networkx(nxg)
assert g.n_nodes == igraph.vcount()
assert g.edges() == igraph.get_edgelist()
assert all(c == 0 for c in g._edge_colors)
igraph = ig.Graph()
igraph.add_vertices(3)
igraph.add_edges(
[(0, 1), (1, 2)],
attributes={
"color": ["red", "blue"],
},
)
with pytest.raises(ValueError, match="not all colors are integers"):
_ = Graph.from_igraph(igraph)
igraph = ig.Graph()
igraph.add_vertices(3)
igraph.add_edges(
[(0, 1), (1, 2)],
attributes={
"color": [0, 1],
},
)
g = Graph.from_igraph(igraph)
assert g.edges(color=0) == [(0, 1)]
assert g.edges(color=1) == [(1, 2)]
def test_edge_color_accessor():
edges = [(0, 1, 0), (0, 3, 1), (1, 2, 1), (2, 3, 0)]
g = Graph(edges=edges)
assert edges == sorted(g.edges(return_color=True))
g = Hypercube(4, 1)
assert [(i, j, 0) for (i, j, _) in edges] == sorted(g.edges(return_color=True))
def test_is_bipartite():
for i in range(1, 10):
for j in range(1, i * i):
x = nx.dense_gnm_random_graph(i, j)
y = Graph.from_networkx(x)
if len(x) == len(
set((i for (i, j) in x.edges())) | set((j for (i, j) in x.edges()))
):
assert y.is_bipartite() == nx.is_bipartite(x)
def copy(self, *, dtype: Optional[DType] = None):
if dtype is None:
dtype = self.dtype
graph = Graph(edges=[list(edge) for edge in self.edges])
return Ising(hilbert=self.hilbert,
graph=graph,
J=self.J,
h=self.h,
dtype=dtype)
def copy(self):
graph = Graph(edges=[list(edge) for edge in self.edges])
return BoseHubbard(
hilbert=self.hilbert,
graph=graph,
J=self.J,
U=self.U,
V=self.V,
mu=self.mu,
dtype=self.dtype,
)
def test_is_connected():
for i in range(5, 10):
for j in range(i + 1, i * i):
x = nx.dense_gnm_random_graph(i, j)
y = Graph.from_networkx(x)
if len(x) == len(
set((i for (i, j) in x.edges)) | set((j for (i, j) in x.edges))
):
assert y.is_connected() == nx.is_connected(x)
else:
assert not nx.is_connected(x)
Lattice,
Edgeless,
Triangular,
Honeycomb,
Kagome,
)
from netket.graph import _lattice
from netket.utils import group
from .. import common
pytestmark = common.skipif_mpi
graphs = [
# star and tree
Graph.from_igraph(ig.Graph.Star(5)),
Graph.from_igraph(ig.Graph.Tree(n=3, children=2)),
# Grid graphs
Hypercube(length=10, n_dim=1, pbc=True),
Hypercube(length=4, n_dim=2, pbc=True),
Hypercube(length=5, n_dim=1, pbc=False),
Grid([2, 2], pbc=False),
Grid([4, 2], pbc=[True, False]),
# lattice graphs
Lattice(
basis_vectors=[[1.0, 0.0], [1.0 / 2.0, math.sqrt(3) / 2.0]],
extent=[3, 3],
pbc=[False, False],
site_offsets=[[0, 0]],
),
Lattice(
def copy(self):
graph = Graph(edges=[list(edge) for edge in self.edges])
return Ising(hilbert=self.hilbert, graph=graph, J=self.J, h=self.h)
def __init__(
self,
hilbert: AbstractHilbert,
graph: AbstractGraph,
J: Union[float, Sequence[float]] = 1.0,
sign_rule=None,
*,
acting_on_subspace: Union[List[int], int] = None,
):
"""
Constructs an Heisenberg operator given a hilbert space and a graph providing the
connectivity of the lattice.
Args:
hilbert: Hilbert space the operator acts on.
graph: The graph upon which this hamiltonian is defined.
J: The strength of the coupling. Default is 1.
Can pass a sequence of coupling strengths with coloured graphs:
edges of colour n will have coupling strength J[n]
sign_rule: If True, Marshal's sign rule will be used. On a bipartite
lattice, this corresponds to a basis change flipping the Sz direction
at every odd site of the lattice. For non-bipartite lattices, the
sign rule cannot be applied. Defaults to True if the lattice is
bipartite, False otherwise.
If a sequence of coupling strengths is passed, defaults to False
and a matching sequence of sign_rule must be specified to override it
acting_on_subspace: Specifies the mapping between nodes of the graph and
Hilbert space sites, so that graph node :code:`i ∈ [0, ..., graph.n_nodes - 1]`,
corresponds to :code:`acting_on_subspace[i] ∈ [0, ..., hilbert.n_sites]`.
Must be a list of length `graph.n_nodes`. Passing a single integer :code:`start`
is equivalent to :code:`[start, ..., start + graph.n_nodes - 1]`.
Examples:
Constructs a ``Heisenberg`` operator for a 1D system.
>>> import netket as nk
>>> g = nk.graph.Hypercube(length=20, n_dim=1, pbc=True)
>>> hi = nk.hilbert.Spin(s=0.5, total_sz=0, N=g.n_nodes)
>>> op = nk.operator.Heisenberg(hilbert=hi, graph=g)
>>> print(op)
Heisenberg(J=1.0, sign_rule=True; dim=20)
"""
if isinstance(J, Sequence):
# check that the number of Js matches the number of colours
assert len(J) == max(graph.edge_colors) + 1
if sign_rule is None:
sign_rule = [False] * len(J)
else:
assert len(sign_rule) == len(J)
for i in range(len(J)):
subgraph = Graph(edges=graph.edges(filter_color=i))
if sign_rule[i] and not subgraph.is_bipartite():
raise ValueError(
"sign_rule=True specified for a non-bipartite lattice"
)
else:
if sign_rule is None:
sign_rule = graph.is_bipartite()
elif sign_rule and not graph.is_bipartite():
raise ValueError(
"sign_rule=True specified for a non-bipartite lattice")
self._J = J
self._sign_rule = sign_rule
sz_sz = np.array([
[1, 0, 0, 0],
[0, -1, 0, 0],
[0, 0, -1, 0],
[0, 0, 0, 1],
])
exchange = np.array([
[0, 0, 0, 0],
[0, 0, 2, 0],
[0, 2, 0, 0],
[0, 0, 0, 0],
])
if isinstance(J, Sequence):
bond_ops = [
J[i] * (sz_sz - exchange if sign_rule[i] else sz_sz + exchange)
for i in range(len(J))
]
bond_ops_colors = list(range(len(J)))
else:
bond_ops = [
J * (sz_sz - exchange if sign_rule else sz_sz + exchange)
]
bond_ops_colors = []
super().__init__(
hilbert,
graph,
bond_ops=bond_ops,
bond_ops_colors=bond_ops_colors,
acting_on_subspace=acting_on_subspace,
)
